1. Technical Field of the Invention
This invention provides an encoding scheme in an optical synchronization system for synchronizing signals which is resistant to stray light noise.
2. Description of the Prior Art
FIG. 1 shows a prior art 3D imaging system that illustrates several fundamental requirements for 3D image projection. First, two two-dimensional (“2D”) images of one scene are displayed, such as by a projection apparatus, one of which is slightly different than the second in terms of a line of sight perspective. These perspectives typically differentiate a left eye view from a right eye view. This normally requires dual image recordation in order to provide the two perspectives, or views, as described above, of the same scene. However, such perspectives could be processed, or manually generated. FIG. 1 illustrates two projectors 101 one of which projects a left eye perspective of a scene while the other simultaneously projects a right eye perspective of the same scene.
Although, simultaneous projection requires two projectors, it is possible to implement a single projector in a 3D imaging system by rapidly alternating the left and right eye perspectives during projection. The present invention does not require that the 3D recordation be done with any specific equipment or number of cameras, only that two perspectives be obtainable or derivable from image data and are capable of being displayed.
Another fundamental requirement of conventional 3D imaging systems is to expose one of the projected perspectives to only one of either the left or right eye and to expose the other of the projected perspectives to only the other eye, such that each projected perspective is seen exclusively with one eye. Thus, with a dual simultaneous projection system, one eye of a viewer will be blocked from seeing the image content from one of the projectors and the other eye will be blocked from seeing the image content from the other projector.
This blocking, often referred to as extinguishing, can be accomplished in two steps. First, each of the simultaneously projected images is polarized at a different polarizing angle by projecting each of them through separately angled polarized transparent media 102. The viewer wears passive polarized eyewear 103 whose lenses are also offset polarized, with respect to each of their polarizing angles, such that one of the lenses will block a first one of the polarized projected images and the other lens will block the second one of the polarized projected images. Prior art methods of generating two different perspectival images include differentiation of the images via red and blue color coding, such as those used with passive eyewear having a blue and red lens.
There have been many attempts to generate 3D image systems. We are concerned here with 3D imaging in systems which use polarization encoding of the left and right eye views, which may be implemented using a switched system Prior art in this field typically relies upon an integrated color wheel/polarizing filter, for example, in systems compatible with digital light processor (“DLP”) or grating light valve (“GLV”) technologies. This creates various problems because as the polarizer rotates it causes the polarization transmission axis of the image to rotate also. In other words, as the polarizer rotates the left and right eye views are only completely isolated for certain precise rotational positions of the polarizer wheel. For other positions of the wheel, the image will contain small components of both the left and right eye views, which cannot be separated by the use of passive polarizing viewing glasses. This results in ghosting of the image; the viewer will perceive a blurred mixture of left and right eye views sometimes, rather than a clear image resulting from total separation of the left and right eye views.
Modern front and rear projection color imaging systems, such as DLP technology, employ multiple color filters to sequentially project elements of a full color image onto a screen. These color filters are typically implemented as segments on a color filter wheel, which spins at a rate synchronized with the input video stream. Typically, this approach uses the three basic video imaging colors (red, blue, and green) in combination with a high brightness white light source. In order to facilitate white balance of the image and correct for certain kinds of image aberrations, a transparent filter segment is often incorporated into the color filter wheel, allowing white light to pass through to the screen.
Existing front and rear projection image systems, such as DLPs, micromirrors, gratings, or related technologies require high intensity white light sources to produce bright images. Despite the use of guiding lenses and optics within these systems, there can be relatively high levels of stray light reflected throughout the interior of the projector package. Some stray light can also leak in from outside the projector through seams in the case. This stray light becomes a problem when we use an optical sensor to synchronize the projector polarizer filter wheel with a stereoscopic imaging device. Stray light can cause false triggering of the sensors and disrupt the required frequency and phase synchronization.
In order to modify these imaging systems so that they support the transmission of stereoscopic three-dimensional images, it is necessary for them to provide alternating left and right eye views. For example, by using a rotating polarizer and having the viewer wear passive eyewear. The alternate eye views are provided by an additional filtering apparatus, which may not be part of the same color filter wheel used in the projector. In this case, it becomes necessary to synchronize the phase, frequency, and possibly other attributes of the rotating color filter wheel with an external stereoscopic imaging element. This synchronization is not necessarily achieved simply by accessing the electronic signals used to control the color filter wheel.
While it is possible to generate stereographic, three dimensional imaging from personal computers and other digital video devices, existing video game consoles lack the standard interface required for generating a video synchronization signal. Shortcomings of systems that employ rotating optics are many. In these systems, it is desirable that the optical device not rotate at a fixed speed. Rotational control improvements are realized by manipulating the speed of the rotating optics at rotational subintervals as dictated by a periodic disturbance signal and cooperative processing apparatus, as described herein.
Published patent application US 2005/0041163A1 describes the use of a segmented polarizer attached to the color filter wheel inside a digital light processor (“DLP”) projector. It does not describe any required relationship between the projector lens optics and the rotating polarizer with respect to polarization sensitivity. Thus, the projection lenses and other optics may corrupt the polarization encoded image signal. Details of the synchronization required between the filter wheel and polarization wheel are not described, nor is there any reference to the distinction between frame sequential and other types of video input. This prior art will not work for all types of video input such as line interleaved video streams. The above-identified patent application is incorporated herein by reference in its entirety.
U.S. Pat. No. 5,993,004 describes a stereoscopic display with a spatial light modulator and polarization modulator, using polarization preserving optics and special control signals for the modulation. As a general statement, this approach does not use rotating or alternating polarizers or digital mirror devices (“DMD”) and DLP technology as our invention does. The above-identified patent is incorporated herein by reference in its entirety.
Published U.S. patent application 2005/0046700A1 describes two video processing devices which process at least four separate sequences of video images for projecting multiple image views on a screen simultaneously. At a high level, this approach does not use rotating or alternating polarizers or DMD/DLP technology as our invention does. The above-identified patent application is incorporated herein by reference in its entirety.
Published U.S. Application 2003/0112507 describes two embodiments for DMD devices, both of which use different rows or columns of the DMD device driven sequentially to provide different eye views of the same image. This approach is not related to the use of rotating or alternating polarizers or DLP technology as our invention is. The above-identified patent application is incorporated herein by reference in its entirety.
Published U.S. application 2003/0214631 describes a projector with a beam splitter to produce two light paths, each of which passes through a fixed polarizer and are later recombined with a special optical system. This approach does not use rotating or alternating polarizers or DMD/DLP technology as our invention does. The above-identified patent application is incorporated herein by reference in its entirety.
U.S. Pat. No. 1,879,793 describes the original motion picture projection system (similar to those later used in IMAX 3D applications) in which the rate of film passing through the projector is synchronized in some fashion with an external polarizing wheel or slides. This approach does not use DLP technology and it is not extensible to DLP technology since it requires special film processing techniques. The above-identified patent is incorporated herein by reference in its entirety.
In the personal computer (“PC”) industry, liquid crystal display (“LCD”) optical shutter glasses have become the standard for cathode ray tube (“CRT”) and projector viewing for color 3D imagery. However, this requires active eyewear (with a miniature liquid crystal monitor or shutter in each lens), as well as requiring a battery and connection to the data source for synchronization purposes. These solutions also tend to be expensive, are only practical for a limited number of users at one time, and tend to induce eye strain after prolonged use. These glasses typically use the Display Data Channel industry standard contained in every modern video adaptor card interface. This data channel signals the glasses that the PC has swapped its eye view.
As a totality, the prior art techniques require modifications internal to the projector filter wheel, and do not provide implementations using legacy systems. Frame sequential and line interleaved technologies are not differentiated in the prior art, which vaguely describes that the signals must be “synchronized” with the polarizer, without providing technical specifications. The prior art does not specify any form for the control circuitry that is not obvious to one skilled in the art.
In general, the prior art requires the projector to use internal optics which are polarization insensitive, since the light polarization must be maintained from the filter wheel through the rest of the projection path. This means that special optics must be used, and polarization sensitive coatings must be avoided, thereby increasing both the complexity and implementation cost. There are no such requirements in the present invention.